This invention relates to internal combustion engines and, in particular, to turbocharged engines having cylinder deactivation, especially for use in vehicles.
It is known in the art relating to automotive vehicle engines that fuel efficiency can be improved by dividing the engine cylinders into two or more groups and deactivating the intake and exhaust valves of one of the cylinder groups for operation of the engine at lower loads where the required power may be developed by the remaining cylinders. It has also been proposed to improve operating efficiency by utilizing a relatively smallsized engine and then increasing its maximum power through turbocharging. In this way, operation under non-turbocharged conditions may be made more fuel efficient by the reduction in throttling needed to operate the engine at the lower load levels required for the greater portion of vehicle driving operation.
To combine these engine concepts, it has been suggested to provide multiple turbochargers, but the complex intake and exhaust systems needed for such arrangements have adversely affected the practicality of such an arrangement.
The present invention provides a compact practical design which combines the advantages of both cylinder deactivation and turbocharging. Preferably, the engine is provided with an even number of cylinders which are divided into two groups such that the firing intervals of the cylinders in each group are evenly spaced. At least one of the groups of cylinders is provided with valve deactivation devices so that operation of this cylinder group may be deactivated while the engine operated on the cylinders of the other group.
Preferably, a single turbocharger is provided for the engine. The turbocharger is of the twin scroll or divided scroll design wherein the exhaust gases from the two groups of cylinders are fed to the turbine wheel through separate paths in the exhaust manifold and through the separate turbine scrolls where the gases impact the turbine wheel from separate outlets within the turbine housing.
When the engine is operated on all the cylinders, the exhaust gases from all the cylinders are utilized to drive the turbocharger to maximize power output when maximum acceleration or speed conditions are required. Otherwise, the engine cylinders operate at lesser loads and the turbocharger rotates freely.
In order to improve engine efficiency at lower loads, a first group of cylinders may be deactivated so that intake and exhaust gas flow through the deactivated cylinders and to the turbine is cut off. However, the second group of cylinders continues to operate at a higher load factor which is more efficient. Exhaust gas from the second, non-deactivated, group of cylinders is fed to the turbocharger and continues to maintain rotation of the turbine wheel during the cylinder deactivation period. Subsequently, when substantially increased power is called for, the deactivated cylinders are returned to full operation and can provide nearly immediate response of the turbocharger, which has been maintained in a rotating condition during the cylinder deactivation operation mode of the engine.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.